AND AVES OF NORTH AMERICA. 



205 



of the premaxillary bono. These lamina; unite just behind the second premaxillary teeth, and form a single prominent 

 keel, which disappears between the first premaxillaries. 



This very fine fragment of one of our largest extinct reptiles, was enclosed in a matrix 

 of soft yellow chalk. It was lent me for introduction into the present synopsis by Prof. 

 Agassiz, of Cambridge, Mass. We look with interest to a complete restoration of this 

 is its matrix is so readily worked. 



""6 



species 



LIODON MITCHILLII, Dekay. 



Geosaurus mitehillii, Dekay, Annals Lye, Now York, III, 140. Bronn, Lethaea Geognostica: nee Mosasaurus 

 mitehiltii, Leidy, Cretaceous Reptiles U. S., et Cope olim, Boston Proceedings, 1869, M. major Dekay. 



Drepanodon impar, Lcidy, Proceed. Acad. Nat. Sci., Phila., 1856, 255. Lestieodus impar, Leidy, Geolog. Surv. 

 N. Ca., 234, figs. 45-0; — fide Leidy. Mosasaurus, Leidy, Cretaceous Reptiles, (15— Tab. XT, 1, 2, 8, 4. 



Tbis species is well characterized by the unequal size of its pterygoid teeth, and by the near equality of some of 

 I hem to the mandibular. Leidy observes that the fang of the first tooth indicates that it was smaller than the second; 

 the second, third and fourth are nearly equal, and largo, then the first and fifth of equal and smaller size, and the sixth 

 to the eighth successively smaller. The teeth from the second to the fourth arc; nearly equal in size to the mandibulars, 

 and with only one divisional cuffing edge. The mandibulars present two, nearly opposite, and faint traces of facets only. 



The case Is entirely different with the M. dekayi, where, as indicated by the measurements, the pterygoids are 

 sub-equal and very much smaller than the mandibulars. 



Other portions of this species are' unknown, hence it may be found at some future time to be the same as some 

 other hove described. In that ease, the name mitehillii will take precedence over any subsequently given. 



From the lower marl bed, Monmouth Co., New Jersey. Prof. Geo. II. Cook. 



LIODON LtEVIS, Owen. 



Macrosaurus Imvis, Owen, Quart. Journ. Gool. Soc. Lond., 1849, 1)80 tab. Leidy, 1. e. 74, 75; (per errorem 

 Wacrosaurus validus Tab. V hujus opens.) 



Portions of three individuals referable to this species have come under my notice, viz: two vertebra; and a radius 

 from Monmouth Co., N. J., found by Dr. Samuel Loekwood; three vertebra from the same county, from O. R. Willis, 

 and a single vertebra from Medford, Burlington Co., from Charles Braddock. The largest individual of the throe is 

 that from Dr. Lookwood's collection, which is nearly equal to the largest of the M. validus, but consider- 

 ably less than that of the M. prorigcr. The cervical has the round articular faces, while the dorsals 



present the vertically ovate form of cup and ball characteristic of the spe- 

 cies. They present also the lino striation of the margins of the diapo- 

 physes and of other articular faces. The radius has tin; outer margin broken 

 away, as represented in the accompanying wooi cut; its humeral articular face 

 is narrow ovate; the carpal curved and stout. The bone is very peculiar, in 

 the presence of a short sub-cylindric process directed inwardly to the ulna, and 

 apparently adapted to it by a, concave artioular face. The radius of Clidastes 



aaid that Of Mosasaurus figured by Leidy (VIII, f. 10, Cretae. Kept.) merely ap- 

 proach or touch the ulna by flu; distal angle. 



Measurements of Supposed Radius. 



Distal width preserved (straight line), 

 Proximal " " 



Width ulnar articular face, 

 A small portion of the external margin preserved, shows a deep incurvature of the outline 



Fig. 49. 



AMhltlCA. PHILO. SOU. — VOL XIV. 52 



